Tom, my grain findings are the same regarding TMX/TMY2. They are exceedingly fine grained, but many people find them almost too fine grained, giving a lower subjective sense of sharpness than their Delta counterparts and more traditional emulsions like FP4+. To some extent this can be remedied by using higher acutance developers such as TFX2 or diluting solvent developers.
FP4+ is definitely a little grainier than Delta, and quite a bit grainier than the TMX films, but typically this doesn't matter in large format, and it is wonderfully sharp with excellent tonality. Probably my favourite film ever for large format. I'd recommend sticking to it, and trying XTOL if you want something a little smoother than DDX.
I should add the contrast you develop for makes a very big difference. If you are going for soft negatives, XTOL can produce the finest grain I have ever seen at 1+1 and even at 1+3 for substantial contractions. But once you get to normal contrast, graininess increases very quickly, even at stock strength and under those conditions I prefer the look of DDX.